258 THE CHEMICAL ANALYSIS OF BUTTER FAT. 



The flask containing the cake of insoluble acids and the paper 

 through which the soluble acids were filtered are allowed to 

 drain and dry for twelve hours, when the cake, together with as 

 much of the acids as can be removed from the filter paper, is 

 transferred to a weighed glass dish. The funnel and filter are 

 then set in an Erlenmeyer flask and the filter washed thoroughly 

 with absolute alcohol. The flask is rinsed with the washings 

 from the filter paper, then with pure alcohol, and these trans- 

 ferred to the glass dish, which is placed in the steam-bath. After 

 the alcohol has evaporated, the residue is dried for two hours 

 in an air-bath at 100 C., cooled in a desiccator, and weighed. 

 It is heated in the air-bath for two hours more, cooled and weighed. 

 If the two weighings are decidedly different, a further heating 

 for two hours must be made. The residue is the total insoluble 

 acids of the sample. 



This method has been submitted to numerous modifications ; 

 Hager adds a known weight of wax, picks out the lump, 

 dries, and weighs it. Fleischmann and Vieth advise that the 

 washing should be continued till at each succeeding washing 

 the coloration produced by the addition of a few drops of litmus 

 solution to a few cubic centimetres of the filtrate is not changed. 

 Cassal has devised an ingenious flask, which has a tap at the 

 bottom so that the liquid can be run off, leaving the fatty acids 

 in the flask ; washing can thus be much expedited, as hot water 

 can be added, the fatty acids shaken up with the water, and the 

 water run off. 



The variation of insoluble fatty acids is from 85-5 per cent. 

 (Bell and Menozzi) to 90-0 per cent. (Reichardt, Cornwall, and 

 others) in genuine butters ; the soluble fatty acids calculated as 

 butyric vary from 7-0 per cent, to 4-0 per cent. Most other fats 

 give about 95-5 per cent, of insoluble fatty acids and traces only 

 of soluble fatty acids. Coconut and palm-nut oils are, how- 

 ever, exceptions to this, yielding from 82 to 85 per cent. 



Estimation of the Mean Combining Weight of the 

 Insoluble Fatty Acids. The fatty acids are dissolved in 

 alcohol, a little phenol-phthalein added, and titrated with alcoholic 

 alkali ; when a pink colour is obtained a small excess is added 

 (2 or 3 c.c.), the solution heated to boiling for ten minutes, and 

 the excess titrated back, as in the Kcettstorfer process. 



The mean combining weight of the fatty acids is calculated as 

 the saponification equivalent. Direct titration of the fatty acids 

 does not yield correct results, owing to the formation of anhy- 

 drides on drying. 



From the difference between the potash absorption, and the 

 potash used for the insoluble fatty acids, an estimation of the 

 soluble fatty acids can be obtained. 



